These share too much yet have very different constructor signatures and
property exposure. Just a clean-up pass as I begin to look at replay
submission.
At first I was planning on making `CompareTo` implemented at
`IRulesetInfo` itself and shared across classes, but turns out it only
implements it explicitly and not allow direct `IRulesetInfo.Equals`
calls.
It messed with my head enough that I decided to just let each class have
its own implementation and only allow same type.